Electronic devices which comprise organic, organometallic and/or polymeric semiconductors are increasing in importance; they are employed in many commercial products for cost reasons and owing to their performance. Examples which may be mentioned here are organic-based charge-transport materials (for example triarylamine-based hole transporters) in photocopiers, organic or polymeric light-emitting diodes (OLEDs or PLEDs) in display devices, or organic photoreceptors in photocopiers. Organic solar cells (O-SCs), organic field-effect transistors (O-FETs), organic thin-film transistors (O-TFTs), organic integrated circuits (O-ICs), organic optical amplifiers and organic laser diodes (O-lasers) are at an advanced stage of development and may achieve major importance in the future.
Irrespective of the particular application, many of these electronic devices have the following general layer structure, which can be adapted for the particular application:    (1) substrate,    (2) electrode, frequently metallic or inorganic, but also made from organic or polymeric conductive materials,    (3) charge-injection layer(s) or interlayer(s), for example for compensation of electrode unevenness (“planarisation layer”), frequently made from a conductive, doped polymer,    (4) organic semiconductors,    (5) optionally further charge-transport, charge-injection or charge-blocking layers,    (6) counterelectrode, materials as mentioned under (2),    (7) encapsulation.
The above arrangement represents the general structure of an organic electronic device, where various layers can be combined, resulting in the simplest case in an arrangement comprising two electrodes, between which an organic layer is located. In this case, the organic layer fulfils all functions, including the emission of light in the case of OLEDs. A system of this type is described, for example, in WO 90/13148 A1 based on poly-(p-phenylenes).
However, a problem which arises in a “three-layer system” of this type is the lack of control of charge separation or the lack of a way of optimising the properties of the individual constituents in different layers, as is achieved in a simple manner by a multilayered structure, for example, in the case of SMOLEDs (“small-molecule OLEDs”).
A small-molecule OLED often comprises one or more organic hole-injection layers, hole-transport layers, emission layers, electron-transport layers and/or electron-injection layers and an anode and a cathode, where the entire system is usually located on a glass substrate. The advantage of a multilayered structure of this type consists in that the various functions of charge injection, charge transport and emission can be distributed over the various layers and the properties of the respective layers can thus be modified separately. This modification enables the performance of the electronic devices to be considerably improved.
A disadvantage of electronic devices which are based on the small molecules described above, i.e. non-polymeric compounds, is the production thereof. Non-polymeric compounds are usually converted into electronic devices by evaporation techniques. This represents a major cost disadvantage, in particular for large-area devices, since a multistep vacuum process in various chambers is very expensive and must be controlled very precisely. Less expensive and established coating methods from solution, such as, for example, ink-jet printing, airbrush methods, roll-to-roll processes, etc., would be a major advantage here. However, the above-described devices comprising small molecules generally cannot be produced in this way owing to the low solubility of the non-polymeric compounds in the usual solvents. Although the solubility of these compounds can be improved by modification, the electronic devices obtained exhibit, however, reduced performance and lifetime compared with the devices obtained by gas-phase deposition.
Thus, for example, WO 2009/021107 A1 and WO 2010/006680 A1 describe organic compounds which are suitable for the production of electronic devices, where these compounds can be processed both by gas-phase deposition and from solution. However, the electronic devices obtained by gas-phase deposition have a more favourable property profile.
Known electronic devices have a usable property profile. However, there is an ongoing necessity to improve the properties of these devices. These properties include, in particular, the lifetime of the electronic devices. A further problem is, in particular, the energy efficiency with which an electronic device achieves the specified object. In the case of organic light-emitting diodes, which may be based both on low-molecular-weight compounds and also on polymeric materials, the light yield, in particular, should be high, meaning that as little electrical power as possible has to be consumed in order to achieve a certain light flux. Furthermore, the lowest possible voltage should also be necessary in order to achieve a pre-specified luminous density.
A further object can be regarded as the provision of electronic devices having excellent performance as inexpensively as possible and in constant quality.
Furthermore, the electronic devices should be capable of being employed or adapted for many purposes. In particular, the performance of the electronic devices should be retained over a broad temperature range.